Determination of phosphorus in molten copper traditionally depends upon chemical or instrumental analysis of solidified samples. The conventional method lacks rapidness and, therefore, is not advantageous from the viewpoint of process control.
Recently, a proposal has been made to determine phosphorus concentration in molten metal (principally iron) by creating an equilibrium between oxygen and phosphorus in the molten metal, determining the activity of oxygen by means of an electrode of a solid electrolyte and calculating the phosphorus concentration (Japanese Laid-Open Patent Publication (Kokai) No. 61-260157). However, it is thought that this method is practically accompanied by considerably difficulty for stabilization of the equilibrium state when it is applied in the commercial production of copper.
Estimation of the phosphorus concentration in copper by measurement of the electric resistance of solid copper materials has hitherto been attempted. However, accurate measurement is not yet achieved since electric resistivity of solid copper is influenced by its metallographical structure and preparation of specimens for accurate measurement of electric resistivity requires an elaborate work.
The measurement of electric resistivity of molten copper, has been attempted since olden days from academic interest. The investigation exclusively relates to pure copper and there is not report relating to phosphorus concentration. Also, technique of the measurement is difficult since high temperature molten metal is handled. Therefore, there has been no report relating to the determination of a specific impurity in molten copper by measurement of electric resistance.
We considered:
(1) Molten metal is free from influence of metallographical structure and is suitable for continuous measurement since shaping, polishing etc. for preparation of specimens are not required. Therefore, rapid and accurate analysis is possible with molten samples, if a technique of measurement is established. PA1 (2) In the academic research, measurement is carried out using a small amount of sample and taking much time. Therefore, it is unavoidable that the sample is contaminated with the material of the electrode and the temperature distribution does not easily become uniform in a small apparatus. These facts will cause errors in measurement. To the contrary, however, an accurate measurement of resistivity would be possible if a large amount of sample can be handled. PA1 (3) The copper deoxidized with phosphorus contains little impurities other than phosphorus. When the phosphorusdeoxidized copper is considered, it can be regarded that the electric resistivity is determined by phosphorus concentration and temperature.
Led by the above-described presupposition, we investigated the relation of phosphorus concentration and temperature with respect to phosphorus-deoxidized copper, containing 0-1000 ppm phosphorus in a temperature range of 1083.degree.-1250.degree. C., and found that there is a relation between phosphorus concentration, electric resistivity and temperature: EQU .rho.=AT+BX+C
wherein A, B and C are constants; p is electric resistivity of molten copper, X is phosphorus concentration and T is temperature. A, B and C are determined for each apparatus.